1. Field of the Invention
The field of the invention relates to electrical switchgear apparatus generally, and more particularly to certain new and useful advances in secondary disconnect devices, of which the following is a specification, reference being had to the drawings accompanying and forming a part of the same,
2. Description of Related Art
Conventional electrical distribution systems employ switching devices, such as for example, circuit breakers in switchgear applications, are conventionally housed in a metal enclosure or “drawout” unit. The drawout units releasably connect the electrical switching devices to an electrical busbar. It is sometimes necessary, such as for scheduled maintenance or testing purposes, to move, or “rack”, the circuit breaker in and out of the enclosure to make and break electrical connection within an electrical power distribution circuit. Conventional drawout units are configured to rack the circuit breakers between a disconnect position, in which the primary contacts or terminals of the circuit breaker are fully disengaged from mating primary contacts within the enclosure, and a connect position in which the primary contacts of the circuit breaker and enclosure are fully engaged. A racking mechanism is typically employed to ensure steady movement of the circuit breaker as it moves between the disconnect and connect positions.
Circuit breakers are also typically equipped with a variety of auxiliary electronic devices and related control circuitry, including switches, motors, solenoids and the like, for providing control of various functions of the circuit breaker such cases, terminals are conventionally arranged on the outside surface of the circuit breaker assembly to provide power to the auxiliary devices and control circuitry, and arranged for automatic connection and disconnection from corresponding mating terminals or contacts arranged within the enclosure. Such corresponding terminals arranged on the circuit breaker and the enclosure are conventionally referred to as “secondary disconnect” terminals or contacts, to distinguish these terminals from the main or “primary” current-carrying circuit breaker and enclosure terminals.
When the circuit breaker is inserted, or racked in, from the disconnect position to the connect position, the corresponding secondary disconnect terminals on the circuit breaker and enclosure must be engaged for power to provided to the auxiliary devices and control electronics. Conversely, when the circuit breaker is removed, or racked out, to the disconnect position, the secondary disconnect terminals must be disengaged. Additionally, it is common to provide a test position, between the connect and disconnect positions of the circuit breaker, wherein the secondary disconnect terminals are engaged, but the primary terminals are not engaged. In such cases, the auxiliary functions of the circuit breaker can be safely tested while the circuit breaker is disconnected from the primary circuit, or “OFF”.
It is generally desirable for the secondary terminals to engage as the circuit breaker is racked in to the test position, and to remain engaged as the circuit breaker continues to be racked in past the test position to the full connect position. Likewise, upon removal of the circuit breaker, it is generally desirable for the corresponding secondary terminals to remain engaged as the circuit breaker is racked out from the connect position back to the test position, but to disengage if the circuit breaker is racked out past the test position to the fill disconnect position. Apparatus for connecting and disconnecting the corresponding secondary terminals of the circuit breaker and enclosure are generally referred to in the art as “secondary disconnect” apparatus. Generally, secondary disconnect apparatus operates such that engagement and disengagement of the secondary terminals is incident to the racking movement of the circuit breaker into and out of its enclosure.
Many conventional secondary disconnect apparatus comprise any number of pairs of corresponding or mating secondary terminals arranged for slidable connection. In many cases, half of each pair of mating secondary terminals includes a conductive surface or receptacle fixedly coupled to the enclosure, while the corresponding half of each pair includes a conductive member fixedly coupled to the circuit breaker. In operation, as the circuit breaker is racked in to the test position, each corresponding pair of secondary terminals makes contact and begin to slide upon each other in electrical connection. As the circuit breaker is subsequently racked past the test position and into the full connect position, each corresponding pair of secondary terminals continue to slide against each other, thereby maintaining contact throughout the entire travel of the circuit breaker. Conversely, when the circuit breaker is racked out of the enclosure, each corresponding pair of terminals disconnect or slide of each other and disconnect.
A known shortcoming of conventional sliding-type secondary disconnect apparatus is that lateral misalignment at or near the test position, between the secondary terminals coupled to the enclosure and the secondary terminals coupled to the circuit breaker prevents proper connection of the secondary conductors.
For example, a known shortcoming of conventional sliding type secondary disconnect apparatus is lateral misalignment of the mating secondary terminals that occurs in the event of a new circuit breaker being retrofit into an existing or legacy enclosure or cubicle. Such lateral misalignment of corresponding secondary disconnect terminals might occur due to inherent tolerance stack-ups in the legacy enclosure and the new breaker being inserted.
For at least the reasons stated above, a need exists for circuit breaker having a secondary disconnect terminal apparatus that enables a lateral movement of the circuit breaker secondary disconnect terminals to allow proper engagement with the corresponding enclosure secondary disconnect terminals.
Also, for at least the reasons stated above, a need exists for a circuit breaker having a secondary disconnect apparatus that is simple, inexpensive, uses few moving parts, and overcomes the aforementioned limitations and deficiencies of known secondary disconnect apparatus.